The present invention relates to integrated optical switching devices, and particularly to such devices for use in high-speed data communication applications, such as in packet switching.
The rapid growth in transmission bandwidths of fiber-optic networks is enabled by, among several critical factors, enhanced switching performance with respect to both switching speed and signal routing. High speed and large port-count switch arrays are becoming progressively important for high-speed data transmissions applications, in particular those supporting packet switching. Various array architectures have been developed as described for example in; R. Y. Awdeh, H. T. Mouftah: Survey of ATM Switch Architectures”, Communications Networks and ISDN systems, Vol. 27, pp. 1567-1613, November 1995 (Elvesier Science); L. Thylen, Integrated Optics in LiNbO3: Recent Developments in Devices for Telecommunications, Journal of Lightwave Technology, Vol. 6, No. 6, June 1988 (pages 847-861); U.S. Pat. No. 4,618,210; U.S. Pat. No. 4,787,693; and International Publication No. WO 99/60434, published 25 Nov. 1999.
However those optical switching devices that support minimum level of route-control processing complexity are more suitable for high-speed switch response. Reduced routing procedures are provided by a family of array architectures, in particular the crossbar and its derivative—the double-crossbar; see for example the R. A. Spanke publication cited above. Other designs are known as the DC, PILOSS, TREE. Recently an SNB (strictly-non-blocking) 16×16 switch-array based on the TREE architecture and implemented in Z-cut LN, was reported [S. Thaniyavarn, Proceedings OFC-97, TuC1]. The TREE based device consists of three parts: fan-out, fan-in, and a mid-section consisting of a large silica/Si substrate, housing the connections between the 256 ports in both the input and output mid-planes.
The above-cited International Publication No. WO 99/60434 reported a recent study of a DC (Deliver and Couple) type array architecture, based on radial layout implemented Z-cut LN and TM guidance, which was shown to support a 16×16 port-count with <10 nSec reconfiguration time. The short switching-speed was aided by the fact that in only 2N switches (out of 2N2 switches) are activated at each of the possible N! route options, and the path setting is achieved merely by straightforward selection of the input-output ports. LN Z-cut substrate accommodates operation in the TM mode, independently of the propagation angle on the substrate, due to the invariance of the refractive indexes at the propagation plane (which is not possible with X or Y cut LN). Since the major electro-optic effect operates perpendicularly to the substrate surface in this case, the switches may be oriented at any angle. In particular, the switches may be designed with curvatures. While the routing procedure is much the same as that of the crossbar architecture (or the double-crossbar), the design has the disadvantage of route-dependent switch paths (i.e. paths having 2 to N+1 switches), which becomes a significant issue when the individual switch losses exceed a certain level.
The double-crossbar architecture, on the other hand, supports a similar path control procedure, and has the advantage of equal switch-paths (always N+1). However, implementation of the double-crossbar by conventional waveguide elements is entirely impractical due to the very large number of waveguide intersections at shallow angles, which induce high losses and cross-talk levels, and in consequence lead to excessive array length.